Mr. Ric Willard

Hyundai-Kia America Technical Center, Inc.

6800 Geddes Road

Superior Township, MI 48198

Dear Mr. Willard:

This responds to your request for an interpretation of how S5.2 of Federal Motor Vehicle Safety Standard (FMVSS) No. 305, Electric-powered vehicles: electrolyte spillage and electrical shock protection, would apply to low-mass, small-energy, high voltage electric vehicle (EV) components that store small amounts of electricity, such as small individual capacitors.1 Specifically, you ask whether these components are “electric energy storage/conversion devices” that are subject to S5.2, Electric energy storage/conversion device retention.


As explained below, our answer is no. Given that the purpose of S5.2 is to protect vehicle occupants from injury by heavy projectiles in a crash, we have determined that low-mass, low- energy, high voltage electronic subcomponents do not fall under the FMVSS No. 305 definition of “electric energy storage/conversion device,” and thus are not subject to S5.2(a).


Regulatory requirements


FMVSS No. 305 specifies requirements for, among other things, the “retention of electric energy storage/conversion devices during and after a crash” (S1). The primary requirement in FMVSS No. 305 relating to component retention is in S5.2(a), which states that, when tested in accordance with S6 of the standard, electrical energy storage/conversion devices “shall remain attached to the vehicle by at least one component anchorage, bracket, or any structure that transfers loads from the device to the vehicle structure,” and that electrical energy storage/conversion devices located outside the occupant compartment “shall not enter the occupant compartment.”


The standard defines the term “electric energy storage/conversion device” as “a high voltage source that stores or converts energy for vehicle propulsion. This includes, but is not limited to, a high voltage battery or battery pack, fuel cell stack, rechargeable energy storage device, and capacitor module” (S4).




1 It is NHTSA’s understanding that these components would be small electrical subcomponents such as capacitors that are attached directly to a circuit board, and have a mass of 300 grams (0.7 pounds) at most.


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NHTSA first established the S5.2 retention requirement as part of a September 27, 2000 final rule that established FMVSS No. 305. 65 FR 57980. The original intent of S5.2 “was to ensure that the battery modules [i.e., energy storage/conversion devices] would not become unattached and become flying projectiles in a crash or subsequent rollover,” causing further damage outside the vehicle. In a later rulemaking, NHTSA added a second purpose to S5.2, which is “to reduce deaths and injuries during and after a crash that occur from the intrusion of electric energy storage/conversion devices into the occupant compartment.” 76 FR at 45442. NHTSA’s concern that an “electric energy storage/conversion device” could intrude into the occupant compartment stems from the fact that high voltage batteries that typically serve as an EV’s primary electric energy storage/conversion device are usually very massive, and therefore would have sufficient momentum to cause serious injuries if not secured in place in a collision.2


NHTSA discussed the applicability of the S5.2 retention requirement in its response to petitions for reconsideration of a June 14, 2010 final rule from Honda and the Association of International Automobile Manufacturers (AIAM). These petitions requested (among other things) that NHTSA clarify what vehicle components fall under the definition of “electric energy storage/conversion device,” and are thus subject to S5.2. As part of NHTSA’s response to these petitions, the agency explained that the S5.2 retention requirement was not intended to apply to low-mass components:


We also agree with Honda and the AIAM that the language of the June 14, 2010 final rule could be interpreted as unintentionally requiring low mass components, such as ducts and vents, to remain attached to the electric energy storage/conversion systems. As previously discussed, today's final rule adds a new definition for “electric energy storage/conversion device,” which includes a high voltage battery or battery pack, capacitor modules, fuel cell stacks, and rechargeable energy storage devices used for vehicle propulsion, but does not include low mass components, such as ducts, vents, and wiring harnesses.


76 FR at 45442. NHTSA has not elaborated on the applicability of the “electric energy storage/conversion device” definition since its response to the Honda and AIAM petitions.




NHTSA has determined that small, low-mass and low-energy electronic subcomponents, such as individual capacitors, do not fall under the definition of “electric energy storage/conversion device,” and thus are not required to remain attached to the vehicle in a crash per FMVSS No. 305, S5.2.





2 This is well illustrated by the vehicle described in your interpretation request. According to the figures provided, the primary energy storage/conversion device (the high-voltage battery) has a mass of 473 kilograms (1,043 pounds). By contrast, all other high voltage components on the vehicle combined have a mass of 133.4 kilograms (294 pounds), and the heaviest individual component (the motor) has a mass of 64.5 kilograms (142 pounds).



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As noted above, the term “electric energy storage/conversion device,” is defined, in part, through a non-exhaustive list of examples. One of the primary characteristics the devices included in this list have in common is that they are constructed from multiple subcomponents to enable them to potentially store a large amount of energy.3 For this reason, the devices in this list tend to be heavy, meaning they pose an unreasonable safety risk due to their momentum if they were to break free from the vehicle. While low-mass electronic subcomponents like individual capacitors could potentially store electrical energy, they are of sufficiently low-energy that they would not pose an unreasonable risk of electric shock in a crash, nor do they contain enough mass to pose an unreasonable risk of impact injury in a crash. Given this key difference between the low-mass items you describe and the components listed in the “electric energy storage/conversion device” definition, NHTSA does not believe low-mass and low-energy electronic subcomponents were intended to be covered by the definition. Thus, the components are not subject to S5.2.


NHTSA’s conclusion that the low-mass and low-energy electronic components you describe are not covered by the definition of “electric energy storage/conversion device” is consistent with the agency’s response to the AIAM and Honda petitions. Although NHTSA did not specifically identify low-mass, low-energy, high voltage electronic subcomponents as excluded from the “electric energy storage/conversion device” definition in its response to the petitions, such subcomponents are more similar to the non-electronic components listed in the petition response than they are to the devices listed in the definition. Like the non-electronic components listed in the petition response, a low-mass, low-energy, high voltage electronic subcomponent would be unlikely to pose a risk of electric shock or risk of impact injury to vehicle occupants in a crash. The fact that a low-mass and low-energy subcomponent is conductively connected to a device that does fall under the “electric energy storage/conversion device” definition does not mean the subcomponent itself falls under the definition.

Although NHTSA does not believe that small electronic components are subject to S5.2, retention methods that unreasonably allow entry of these electronic components into the passenger compartment in a crash could pose an unreasonable risk to safety. Efforts should be taken to prevent these components from entering the passenger compartment in a crash.


If you have further questions, you may refer them to Daniel Koblenz of my staff at (202) 366- 2992.






                                                                                                                                                                                               Digitally signed by ANN ELIZABETH CARLSON

                                                                                                                                                                                                                                                                       Date: 2022.05.31 13:11:20



Ann Carlson

Chief Counsel




Dated: 5/31/22

Ref: FMVSS No. 305









3 For example, a “capacitor module,” which is one of the illustrative examples listed in the definition of “Electric energy storage/conversion device,” is a device that is comprised of arrays of several capacitors.